From under- +‎ lease.

• IPA^(key): (noun) /ˈʌndə(ɹ)ˌliːs/
• IPA^(key): (verb) /ˌʌndə(ɹ)ˈliːs/

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underlease (plural underleases)

1. (property law) Synonym of sublease.

   Synonyms: sublease, subtenancy, undertenancy, subletting, underletting, (informal) sublet, underlet

underlease (third-person singular simple present underleases, present participle underleasing, simple past and past participle underleased)

1. (property law, informal) Synonym of sublet.

   Synonyms: sublet, underlet, (informal) sublease, subtenant

• “underlease”, in Webster’s Revised Unabridged Dictionary, Springfield, Mass.: G. & C. Merriam, 1913, →OCLC.

• unreleased, unresealed