Each clue contains a superfluous word, the first letters of which [NUMBERS AREN’T INCLUDED IN WORDPLAY] indicate how to complete the 13 solutions marked *

Across

1* Fourier [Not] 4 + /I(d)E(st)/R(ight) [Joseph Fourier, d. 1830]

5* at worst [Uranium] 2 in TSAR (anag)

9 vison [Maybe] VIS(i)ON [US mink]

10* freighter [British] FR(ench)/8/ER

11 rifle green [Enemy] R(oyal) + FEELING (anag) over R(oyal)E(ngineers)

12 limb [Risks] LIMB(o)

14* dreadnought [Sailor] D(eparted)/READ/0

18 overearnest [Acting] (getting) over Ernest (hom) [Ernest Borgnine, d. 2012]

21 east [Roast] (f)EAST

22 chaste tree [Energy] EACH STREET (anag)

25 severance [Nativity] S(econd)/EVE/RAN/C(of)E

26* sixte [Tiny] 6/TE(llurium)

27* canines [Icelandic] C(old)/A</9>S

28* threeps [Nationalist] 3/P(olicie)S [Scottish dialect]

Down

1* fivers [Contralto] 5/R(i)S(e) [bank notes]

2 unsafe [Looks] U(nited)//FANS(anag)/(fi)E(ld)

3 innuendoes [Unreliably] IN/NU N/DOES

4 refer [Debit] palindrome

5 âme perdue [Exists] A/MEP/RUDE(anag)/E(Spain)

6 wage [Duet] double def

7 rattings [Increase] RAT INGS

8 terabyte [Nobody] Y(why) in A BETTER (anag)

13 tortfeasor [Wasters] T(ime) ) + ARE SORT OF (anag)

15* earphones [Ominous] 1 in PHRASE (anag)

16* honey-sac [Receive] 1/(mone)Y in CASH (rev)

17* gets even [Dane] G(r)E(a)T + 7

19 wraxle [Power] WAR(anag)/XL(40)/E(nglish) [West Country dialect]

20* tenets [Lawyers] 10/SET(anag)

23* stent [Albans] S<10>T

24 bran [Your] BRA(i)N