say it: UHN-dur-pin
underpin is a verb meaning "support from beneath". It carries 2 recorded senses.
support from beneath
support with evidence or authority or make more certain or confirm
“The stories and claims were born out by the evidence”
Forms marked · are formed by the regular rule rather than recorded in the source data. English keeps a few hundred irregulars and the rest follow the pattern, so the rule is right far more often than not — but it is a rule, and the mark says so.
Definitions, synonyms and semantic relations for underpin come from Princeton University’s WordNet. The pronunciation comes from the CMU Pronouncing Dictionary. Commonness is measured against a corpus of everyday English. Full sources and licences.