underportion means the lower portion of something; the underneath. Lexicurio rates it Rare gem — a strength score of 82 out of 100.
Etymology
From under- + portion.
noun
- The lower portion of something; the underneath.“New relay rooms have been provided at Maidenhead West, Twyford and Reading Main Line East signalboxes; in the latter case an underportion of the building was reconstructed to provide additional rooms for the relay equipment and a diesel standby generator.”