(a particular) expert knowledge and skill

knowledge

a part of a fish with which it breathes; a liquid measure, one-quarter of a pint (0.14 litres)

opening

either of the bone structures (lower and upper jaw) containing the teeth; the part of a tool, machine, etc between which things are gripped or crushed

bones of chin

one or other of the fleshy edges of the mouth

edge, brink

the lower jaw in mammals and fishes

bones of chin

the opening through which animals take in food; an opening or way out (of a bag, bottle, tunnel, cave, river etc)

opening

the quality of being skilled

ability, skilfulness