I am hoping I can use the collective knowledge of the forum to piece together some history. I'm wondering where the terms pseudo-isotopy and concordance originated, in their modern forms as used in manifold theory, to denote a diffeomorphism of a product manifold $M \times I$ that's the identity on all but the one boundary face $M \times \{1\}$.
Doing a MathSciNet search I see pseudo-isotopy appearing in some detail in Milnor's h-cobordism notes (1965), where he mentions the synonym "I-cobordism" was used by Munkres and concordance by Hirsch. Without the hyphen pseudoisotopy appears in a 1959 paper of R.H.Bing, but he appears to use the term as if it were already in common usage. A search for concordance gives an even earlier paper, 1948 by Youngs.
None of these papers give the appearance of being first-usage, as the term appears to be used too casually. Perhaps I am misinterpreting one of these authors. There are some sources MathSciNet does not know, like the Soviet journals of the time. Perhaps the term originated in one of those unindexed journals, or some other non-English language journal. That said, the community was small so perhaps the decision to use the terminology was made collectively, at a conference.
I would presume the connection between pseudo-isotopy and the h-cobordism theorem was made by one of Smale, Whitney or Milnor as it was solidified by the time Milnor's lecture notes were written, and this was a perspective favoured by Whitney.