Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
ălesco, ĕre, v. inch. n. [alo], to grow up, increase (only ante-class.), Varr. R. R. 1, 44, 4; 2, 4, 19: alescendi cacumen, * Lucr. 2, 1130.