su SU cmavo

erase to start of discourse or text; drop subject or start over.

On grammatical class:

su
erase to start of discourse or text; drop subject or start over.

In definition:

si'oi
erases a SI, SA or SU cmavo; is to "redo" as SI/SA/SU is to "undo".
cmavrsu
x1 is the selma'o "SU".
gugdesu'u
x1 is the country with the code ISO-3166 SU (USSR) for people x2.

In notes:

vicma'o
x1 is an eraser word
de'ai
default value (re)specification/(re)assignment/(re)definition/over-write; set new default value (terbri-specific; permanent)
su'u'u'u'u'u'u'u
erasure word: delete everything that was ever said in Lojban.
nebmaugi
x1 is a part of Lojban text representing rule 'null'