The two words can be treated as synonyms, but when put together as
hetupaccaya, each has a different meaning. The combined word
hetupaccaya means condition and cause, or the efficacy of kamma.
Quote (PED paccaya): paccaya became synonymous with our "relation,"
understood in a causal sense, hetu meaning condition, causal
antecedent, and 23 other relations being added as special modes of
causality.
Since this compound is not found in the Suttapitaka at all, I have
decided to skip the example this week. But I'd appreciate an
elaboration on the meaning of the term.