Clue Help

[hankir]

There is an extra word in the clue.

Oppressive Liberian tyrant periodically cross (3)
?SO

I think Liberian is the extra word.
Periodically cross will be COS.

Help appreciated.

[Lie-in King]

Dso (alt. sp. of 'Zho') - 'D(e)s(p)o(t)'

Chambers lists it, the meaning's here -

http://www.collinsdictionary.com/dictionary/english/zo_1

[hankir]

Thanks Lie-in King.
This was a tough one.
Usually the word/phrase that has to be regularly looked at is in the clue.
This one required to find a synonym before solving it.

[Lie-in King]

Glad I could help :-)