双節棍[nunchaku] nunchaku (two linked fighting sticks)
一双[issou] pair (esp. of folding screens)
一卵性双生児[ichiranseisouseiji] identical twins
双紙[soushi] written work (esp. a bound text, as opposed to a scroll)
自己双対[jikosoutsui] self dual

双刃[moroha] double-edged
双暗車[souansha] twin propellers
双殻類[soukakurui] bivalves
双眼[sougan] both eyes

一眼[ichigan] one eye
一眼レフ[ichiganrefu] single-lens reflex camera
一隻眼[issekigan] sharp eye
遠眼[engan] farsightedness
遠眼鏡[toomegane] spectacles for far-sightedness

凹眼[ougan] cavernous eyes
凹眼鏡[ougankyou] concave glasses
開眼[kaigan] enlightenment
眼下[ganka] under one's eyes
眼科[ganka] ophthalmology