On the width of verbal subgroups of the groups of triangular matrices over a field of arbitrary characteristic

The width [Formula: see text] of the verbal subgroup [Formula: see text] of a group [Formula: see text] defined by a collection of group words [Formula: see text] is the smallest number [Formula: see text] in [Formula: see text] such that every element of [Formula: see text] is the product of at most [Formula: see text] words in [Formula: see text] evaluated on [Formula: see text] and their inverses. Well known that every verbal subgroup of the group [Formula: see text] of triangular matrices over an arbitrary field [Formula: see text] can be defined by just one word: an outer commutator word or a power word. We prove that [Formula: see text] for every outer commutator word [Formula: see text] and that [Formula: see text] except for two cases, when it is equal to 2. For finitary triangular groups, the situation is similar.