GMAT Vocabulary Flash Cards @ englishpdf.com and englishteststore.com File 013 Achillean (adj) Invulnerable achromatic (adj) Colorless, acid (n) A sour substance acidify (v) To change into acid acknowledge (v) To recognize; to admit the genuineness or validity of acknowledgment (n) Recognition acme (n) The highest point, or summit acoustic (adj) Pertaining to the act or sense of hearing