I frequently encounter “vs” words like:
- prodigal vs prodigious
- ingenuous vs ingenious
- affluent vs effluent
These words are very similar but not identical in spelling, and have different meanings.
(Since the words are not identical there are not heteronyms)
Is there any term that describes such pairs of words?
The only word to describe what you are asking is paronym.
Bear in mind ‘wisdom’ is a paronym of ‘wise’ which differs by more than just one character unlike the examples in your question.
There isn’t one word to describe exactly what you have asked but hopefully this answer will suit your needs.
As mentioned by John Lawler in the comments under your question the term is rarely used. In fact it’s so rare that the spell-checker software on my Google Chrome web browser doesn’t recognise it.
See http://oxforddictionaries.com/definition/english/paronym for in-depth details.