inaudibly.

Too quietly or unclearly to be heard.

Use it for

Words that belong together

• speak inaudibly
• murmur inaudibly

On the page

His final words fell inaudibly beneath the engine noise.

Usage notes

Primary category: literary / elevated general. Forms: Invariable adverb. Legacy lexical fields mirror sense 1 only. Use numbered sense fields for all meanings. Established modern English lexical item. No separate regional spelling or grammatical inflection entry. Writing functions: description, character. Commonness: moderately common.