Glabella
1. The small smooth area on the human forehead between the eyebrows just above the nose.
Also …
2. The smooth median portion of the cephalic shield of a Trilobite.

Being an anatomical term the word is needless to say derived from the Latin. The OED records the first use in 1598.

Glabrous
Free from hair, down, projections or pubescence; having a smooth skin or surface.
And hence used jocularly for anything smooth.
Now used only as a scientific term.
The origin in the Latin glaber, without hair, smooth, bald.
The OED records the first usage by Wilkins in 1640 who applied it to the orb of the Moon.

Tintinnabulation
A ringing of a bell or bells, bell-ringing; the sound or music so produced. The lingering sound that occurs after a bell has been struck.
The OED gives the first recorded use as late as 1831 and is ascribed to Edgar Allen Poe in his poem The Bells.
Oh and the word derives from the Latin tintinnābulum, a bell.
Isn’t it just a wonderful onomatopoeic word?

Offing
Yes, offing is a responsible, adult word! And not just in the phrase “in the offing” which is now perhaps its most common usage. It is actually a nautical term …
1. The part of the visible sea distant from the shore or beyond the anchoring ground.
2. A position at a distance off the shore.

Hence, by analogy to a ship some way off shore but visible, that phrase “in the offing” meaning something that is close-ish to hand and yet some way distant.
The OED gives the first recorded use in 1627.

Varmint
1. Vermin. An animal of a noxious or objectionable kind.
  
2. An objectionable or troublesome person; a mischievous boy or child.
3. Knowing, clever, cunning.
Also, 4. A sporting amateur with the knowledge or skill of a professional.

The OED gives the derivation for meanings 1 & 2 as a variant of vermin with excrescent. Although the first recorded use is in 1539 the word is said to be rare before about 1825. There is apparently no obvious connection between the word as used in meanings 1 & 2 and that of meanings 3 & 4, which I find hard to believe.

Earlier in the week I came across a wonderful list of 18 obsolete words, which never should have gone out of style.
They’re all wonderful, but here’s a selection …
Snoutfair: A person with a handsome countenance.
Pussyvan: A flurry, temper.
Wonder-wench: A sweetheart.

Spermologer: A picker-up of trivia, of current news, a gossip monger.
Tyromancy: Divining by the coagulation of cheese.
Beef-witted: Having an inactive brain, thought to be from eating too much beef.
Resistentialism: The seemingly spiteful behaviour shown by inanimate objects.
Bookwright: A writer of books; an author; a term of slight contempt.

And I think my favourite of all …
With squirrel: Pregnant.
English is such a wonderful language!

Chatoyant
Having a changeable, undulating, or floating lustre, like that of a cat’s eye in the dark.
Hence also a chatoyant stone or gemstone, such as the cat’s-eye.

From the French present participle of chatoyer, to shimmer like cats’ eyes; from chat, cat.
The OED records the first use in 1798 in a scientific description of crystals.

Hallux, plural halluces.
1. The innermost or first digit on the hind foot of certain mammals. In humans the hallux is the big toe.
2. The equivalent digit of a bird, reptile or amphibian. In birds it is often directed backward.

The hallux corresponds to the pollex, or thumb, of the fore limb.
According to the OED the first recorded use was in an anatomy book of 1831.
The suggestion is that it is a medieval Latin blend of allus, hallus (thumb) and hallex (big toe).

Baculm
The os penis, a bone found in the penis of many placental mammals. It is absent in humans, but present in primates such as the gorilla and chimpanzee. The bone aids sexual intercourse by maintaining sufficient stiffness during sexual penetration. It is also suggested that certain shapes may assist in the removal of a rival’s sperm from the female vagina.
The female equivalent is the os clitoridis, a bone in the clitoris.

Walrus baculum, approximately 22″ (56cm) long

The size and shape of the baculum varies greatly between even closely related species and is often used as an aid in identification of species. But no-one knows why it is absent in humans, and relatively rudimentary in other great apes, compared with many other mammals.
The word is derived from a Latin for a cudgel, sceptre, staff or stick.