Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
* sum-mūto (subm-), āre, v. a., to change, interchange, substitute one thing for another: hanc ὑπαλλαγὴν rhetores, quia quasi summutantur verba pro verbis, μετωνυμίαν grammatici vocant, quod nomina transferuntur, Cic. Or. 27, 93.