A verbal lexeme is monovalent if it has only a single °argument position in its °valency.
"Monovalent" is defined with respect to "valency" here, i.e. with respect to arguments, not semantic roles (as in Croft's definition).
monovalent event (SEM) = an event with a valency of one – that is, with one central participant role. Example: sleeping is a monovalent event. (Section 6.1.2) morphological causative