oojah capivvy

Etymology
. Perhaps from  ḥujjat kāfī fīhi (“argument is sufficient”); compare. Sornig (see quotations below) suggests derivation from, but seems to be alone in this suggestion. Attested from the 1910s, often described as soldiers’ or sailors’ slang.

Noun

 * 1)  Something that one cannot name or does not know the name of; a whatsit.