It's
Stra, standing for 'Stranger'. On its own
Stra usually means 'not a blood relative', but
NC in the next column is probably 'natural child'.
A range of detailed 'Stranger' options is given here …
https://www.nationalarchives.gov.uk/help-with-your-research/research-guides/death-duties-1796-1903/8.2 Abbreviations used to describe relationships (under ‘consanguinity’ in the register)Str or Stra or Strag = stranger in blood
Stra BL = stranger, brother-in-law
Stra DL = stranger, daughter-in-law
Stra NC = stranger, natural child (that is, illegitimate)
Stra ND = stranger, natural daughter (that is, illegitimate)
Stra NS = stranger, natural son (that is, illegitimate)
Stra NC (of a daughter) = stranger, illegitimate child of a daughter
Stra NC (of a son) = stranger, illegitimate child of a son
Stra (sent) = stranger, servant of deceased
Stra SL = stranger, sister-in-law or stranger, son-in-law
Stra or ‘son’ = stranger, natural son (that is, illegitimate)
Stra or ‘daughter’ = stranger, natural daughter (that is, illegitimate)