Etymology 1

By analogy with past tenses and past participles ending in "-unk", such as drunk and sunk

Verb

thunk

1. Who would have thunk it?

Interjection

1. Representing the sound of the impact of a heavy object striking another and coming to an immediate standstill, with neither object being broken by the impact.

Verb

1. to strike against something, without breakage, making a "thunk" sound

   I was thunked on the head by his stick.

Etymology 3

Claimed by the inventors to be from the supposed past tense, being coined when they realised after much thought (whence "thunk") that the type of an argument in ALGOL 60 could be predetermined at compile time; not, as is sometimes claimed, from the interjection, being the supposed sound made by data hitting the stack or an accumulator

Noun

1. a delayed computation
2. In the Scheme programming language, a function or procedure taking no arguments.
3. a mapping of machine data from one system-specific form to another, usually for compatibility reasons, such as from 16-bit addresses to 32-bit to allow a 16-bit program to run on a 32-bit operating system