Clueless means having no idea at all. Completely clueless, clueless about it, a clueless response.
It is informal and dismissive, and it says the person does not know rather than that they are stupid — which is a slightly kinder charge, though it rarely sounds it. It is very common in British speech. Note that the word depends on clue, which comes from clew, a ball of thread — the thread Theseus used in the labyrinth, so having no clue is having no thread to follow.
1adjectivecluelessHaving no idea at all.
“I'm completely clueless about cars, so I just nod when the mechanic talks.”
clueless is a state of not knowing.
Proto-Indo-European
*glew- — to ball up, clump together; lump, swelling
Proto-Germanic
*kliuwīną
Proto-West Germanic
*kliuwīn — ball, clump
Old English
clēowen
Middle English
clew
English
clue
English, today
clueless
Built from
From clue + -less. clue Variant of clew (“a ball of thread or yarn”), from Middle English clew, clewe, clowe, clue, clwe, clyw, clywe, from Old English clēowen, clīewen, clīowen, clīwen, clȳwe, clȳwen (“ball, sphere; skein”), from Proto-West Germanic kliuwīn (“ball, clump”), from Proto-Germanic kliuwīną, klewô (“bale, ball, clump, mass”), from Proto-Indo-European glew- (“to ball up, clump together; lump, swelling”). Sense evolution with reference to the one which the mythical Theseus used to guide him out of the Minotaur's labyrinth. More at clew. 2 Cognate with cim khnaul (“ball of yarn”), Dutch kluwe, kluwen (“ball thread or yarn, clew”), German Knäuel (“ballyarn; tangle”), Norwegian Nynorsk kljå (“a loom weight”); also Sanskrit ग्लौ (“the moon; camphor; the earth”).
Etymology from Wiktionary, CC BY-SA