Past tense of delve; dug or investigated carefully or thoroughly.
From Old English 'delfan' (to dig), related to Germanic roots. The sense shifted from literal digging to figurative investigation by the 14th century, as in 'delve into' a mystery.
Ancient languages had separate words for different kinds of digging—'delve' originally meant digging with a spade, while 'dig' was more general. We kept the fancier word specifically for intellectual digging.
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