acorn tube(n = noun.artifact) - a small vacuum tube; used at high frequencies;
is a kind of electron tube, thermionic tube, thermionic vacuum tube, thermionic valve, tube, vacuum tube

acorn, acorn barnacle, acorn cup, acorn squash, auditory tube, blow tube, boob tube, boron counter tube, bronchial tube, calyx tube, capillary tube, cartilaginous tube, cathode-ray tube, color television tube, color tube, color tv tube, colour television tube, colour tube, colour tv tube, counter tube, crookes tube, digestive tube, electron tube, endotracheal tube, eustachian tube, fallopian tube, gas-discharge tube, geiger tube, geiger-muller tube, geissler tube, germ tube, glow tube, hittorf tube, inner tube, ionization tube, kundt's tube, lenard tube, nasotracheal tube, neon tube, neural tube, picture tube, pitot tube, pitot's tube, pitot-static tube, pl'81cker tube, pollen tube, proportional counter tube, rear of tube, rectifying tube, sea acorn, sieve tube, speaking tube, static tube, television pickup tube, television tube, television-camera tube, test tube, thermionic tube, thermionic vacuum tube, torpedo tube, tricolor television tube, tricolor tube, tricolour television tube, tricolour tube, tube, tube foot, tube railway, tube well, tube wrench, uterine tube, vacuum tube, venturi tube, vortex tube, water tube, x-ray tube