Lewis considered this as a generalization of the Brønsted definition, so that an acid is a chemical species that accepts electron pairs either directly or by releasing protons (H+) into the solution, which then accept electron pairs.
lˈuːɪs kənsˈɪdɚd ðɪs æz ɐ dʒˌɛnɚɹəlᵻzˈeɪʃən ʌvðə bɹˈɑːnstᵻd dˌɛfɪnˈɪʃən, sˌoʊ ðæt ɐn ˈæsɪd ɪz ɐ kˈɛmɪkəl spˈiːsiːz ðæt ɐksˈɛpts ᵻlˈɛktɹɑːn pˈɛɹz ˈiːðɚ dᵻɹˈɛktli ɔːɹ baɪ ɹᵻlˈiːsɪŋ pɹˈoʊtɑːnz ˈeɪtʃ plˈʌs ˌɪntʊ ðə səlˈuːʃən, wˌɪtʃ ðˈɛn ɐksˈɛpt ᵻlˈɛktɹɑːn pˈɛɹz.