Xenodochium
A house of reception for strangers and pilgrims; a hostel, guest-house, especially in a monastery.
From the Greek ξένος a stranger + δέχεσθαι to receive.
First recorded by the OED a in use as late as 1612.

Griffonage
Scribble. Illegible handwriting.

This is an affliction with which I have, according to my father, been blessed from the earliest age — my handwriting always did look like an arthritic spider had crawled out of the inkpot and it is still getting worse!
The derivation is from the French griffonage, griffonner, to write badly or scrawl. The OED records the first documented usage as 1832.

Pinniped
1. Belonging to the Pinnipedia, a suborder of carnivorous aquatic mammals that includes the seals, walruses and similar animals having fin-like flippers for locomotion.
2. A mammal of the suborder Pinnipedia.

Like many such scientific terms the word is derived from the Latin and was first used in 1842.

Aiguillette
An ornamentation worn by certain military officers consisting of cords with metal tips.

This is a surprisingly recent import from French, with the OED giving the first recorded English usage is 1816.

Hypergamy
In anthropology and ethnology …
1. A custom that forbids a woman to marry a man of lower social status.
2. Any marriage with a partner of higher social status.
According to the OED the term was first used by W Coldstream circa 1883.

Grenade
1. A pomegranate. (Now obsolete)
2. A small bomb or explosive missile that is detonated by a fuse and thrown by hand or shot from a rifle or launcher.
3. A glass container filled with a chemical such as tear gas that is dispersed when the container is thrown and broken.

The word is derived from the French grenade, and Spanish & Portuguese granada, a pomegranate, which the original grenades were supposed to resemble.
Hence grenadine, a syrup made from pomegranate, the island of Grenada, and the Grenadier Guards.
The OED records the first English use (with meaning 1) in 1532.

Sir Walter Scott coined the word “freelance” in Ivanhoe, using it to refer to a mercenary knight with no allegiance to one particular country and who instead offers his services for money.
From ‘A’ to ‘ampersand’, English is a wonderfully curious language; Guardian; 15/02/2014

Until as recently as the early 1900s, “&” was considered a letter of the alphabet and listed after Z in 27th position. To avoid confusion with the word “and”, anyone reciting the alphabet would add “per se” (“by itself”) to its name, so that the alphabet ended “X, Y, Z and per se &”. This final “and per se and” eventually ran together, and the “ampersand” was born.
From ‘A’ to ‘ampersand’, English is a wonderfully curious language; Guardian; 15/02/2014

Haruspicy
Divination by natural phenomena, especially from inspection of the entrails of animal sacrifices.

Cataphract
1. Defensive armour used for the whole body and often for the horse, also, especially the linked mail or scale armour of some eastern nations.
2. A horseman covered with a cataphract.
3. The armour or plate covering some fishes.

The word is derived from the Latin cataphractes, Greek καταϕράκτης, a coat of mail; also from Latin cataphractus, Greek κατάϕρακτος, clad in full armour.
Surprisingly the OED gives the first recorded usage in 1581.