Here's what rhymes with efficacious.
gracious spacious efficacious audacious capacious fallacious herbaceous sebaceous vexatious vivacious voracious salacious tenacious ungracious flirtatious loquacious mendacious ostentatious Words that almost rhyme with efficacious
cases basis gazes faces bases phases phrases races spaces raises vases laces chases glazes mesas places traces praises braces fireplaces paraphrases metastases homeostasis famous patience courageous cadence heinous hiatus fracas patients greatness stainless nameless valence faithless painless sameness shameless shapeless waitress bailiffs baseless faceless lateness plainness graceless weightless payments impatience surveillance claimants contagious fragrance outrageous abeyance blameless tasteless faintness ignoramus quaintness straightness statements acquaintance conveyance engagements platelets reagents assailants pavements strangeness basements mandamus vagrants inpatients arrangements advantageous attainments placements repayments complainants complaisance misstatements displacements entertainments replacements disadvantageous rearrangements emplacements