Fo'c'sle

The forecastle, pronounced - as sailors say it - fo'c'sle, IPA: /ˈfəʊk s^əl/ - is the raised deck commonly found at the front of a ship. (In sailing ships, it was forward of the foremast.) Spelling note: the word fo'c's'le being aphetic for 'fo[re]c[a]s[t]le', it is written with different uses of the apostrophe: fo'c'sle (OED's preference), fo'c's'le, fo'cas'le and so on.

The etymology may be of interest.

In the days when hand-to-hand fighting was the centre of naval warfare and guns were not yet in use, the forecastle was a tall defensible structure which was used to house archers, grappling irons and other weapons to suit that style of combat. It was a castle built in the fore part of the vessel. (It was echoed by a similar, but usually taller, structure in the after part of the vessel: the aftercastle (sometimes aftcastle or sterncastle)). When guns became the predominant weapon at sea, and manoeuvrability therefore increased in importance, the disadvantage of such bulky obstructions and their wind resistance became obvious, and they declined in importance. However, it remained helpful to have a raised deck towards the front of the vessel, for handling forward-firing ordnance and for handling anchors, mooring ropes and headsails. (In the days of steam battleships, it helped raise the forward gun turrets above the breaking seas through which power drove the vessel.)

It became the norm in ships for the crew to be berthed apart from the officers, and the space beneath this raised deck became the bunk-room for the crew. Hence a fo'c'sle man is a common sailor; a fo'c'sle yarn (story) and a fo'c'sle song are the stories and music with which such ordinary sailors may entertain each other.