FIN - One of the appendages of a fish, used to propel itself and to manoeuvre/maneuver.
FIR - A conifer of the genus Abies.
FUN - Enjoyable, amusing.
FUR - Hairy coat of various mammal species, especially: when fine, soft and thick.
INN - Any establishment where travellers can procure lodging, food, and drink.
NUN - A member of a Christian religious community of women who live by certain vows and usually wear a habit, in some cases living together in a cloister.
REF - Referee.
FEN - A type of wetland fed by ground water and runoff, containing peat below the waterline.
FERN - Any of a group of some twenty thousand species of vascular plants classified in the Division Pteridophyta (formerly known by some as Filicophyta) that lacks seeds and reproduces by shedding spores to initiate an alternation of generations.
FINE - Of superior quality.
FIRE - A (usually self-sustaining) chemical reaction involving the bonding of oxygen with carbon or other fuel, with the production of heat and the presence of flame or smouldering.
NINE - A numerical value equal to 9; the number occurring after eight and before ten.
RUIN - Construction withered by time.
REIN - A strap or rope attached to the bridle or bit, used to control a horse, animal or young child.
RIFE - Widespread, common (especially of unpleasant or harmful things).
FINER - Comparative form of fine: more fine.
INNER - Being or occurring (farther) inside, situated farther in, located (situated) or happening on the inside of something, situated within or farther within contained within something (inner door, inner room, inner sanctum, inner surface).
INFER - To show; to manifest; to prove.
INURE - To take effect, to be operative.
FUNNIER - Comparative form of funny: more funny.