Forecastle

Forecastle (pron. fowk-sul; commonly abbreviated "fo'c's'le") refers to the upper deck of a sailing ship forward of the foremast, or the forward part of a ship with the sailors' living quarters. Related to the latter meaning is the phrase "" which denotes anything related to ordinary sailors, as opposed to a ship's officers.

The syncope of the word, fo'c'sle or fo'c's'le (/ˈfoʊksəl/ or /ˈfɒksəl/), is common among nautical terms, but the position of apostrophes is not universally agreed. The positioning of the apostrophes represents silent letters, thus fo[re]c[a]s[t]le.

In medieval shipbuilding, a ship of war was usually equipped with a tall, multi-deck castle-like structure in the bow of the ship. It served as a platform for archers to shoot down on enemy ships, or as a defensive stronghold if the ship were boarded. A similar but usually much larger structure, called the aftcastle, was at the aft end of the ship, often stretching all the way from the main mast to the stern.

Having such tall upper works on the ship was detrimental to sailing performance. As cannons were introduced and gunfire replaced boarding as the primary means of naval combat during the 16th century, the medieval forecastle was no longer needed, and later ships such as the galleon had only a low, one-deck high forecastle. Sailors stationed on the forecastle, or "forecastle men," were responsible for handling the headsails and the anchors. In the Royal Navy of the 17th and 18th centuries, these roles were reserved for older seamen who lacked the agility to go aloft or take other more strenuous duties aboard.

...
Wikipedia