The word Osa is misspelled against Ossa, which is plural of "Os"
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Ossa has double "ss" is mispronounced as "s"
Remember double 'SS' in between the strings o & a which should not be misspelled with single 'S'
Wrong Spelling:  o-s-a 
Correct Spelling:  o-ss-a 
Browse incorrect spellings of Ossa to spell it good.