say it: UHN-dur-lahyn
underline is a verb and noun meaning "give extra weight to (a communication)". It carries 3 recorded senses.
give extra weight to (a communication)
“Her gesture emphasized her words”
draw a line or lines underneath to call attention to
a line drawn underneath (especially under written matter)
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 underline 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.