He plans to 'thin' (out) the young carrots in the garden. [=to remove some of them so that there is more room between the remaining carrots]
His hair is a little 'thin' on top. = He's a little 'thin' on top. [=he does not have a lot of hair on the top of his head]
The bank's decision to raise rates could be 'the thin end of the wedge'. [=many other banks may also decide to raise rates]
(..) You marry for love. You're a good husband. Children arrive, years depart. And all of a sudden, your wife grows old and tired. And her hair is thin. And her body... And you yourself, you still have your vigor! And then you find yourself a martyr to distraction by so many women. (..)2012 Anna Karenina