The headword is the genitive singular of the noun spekoula/twr, a transliteration of Latin speculator, evidently quoted from somewhere (and here, uniquely with omega as the penultimate vowel).
The Suda entry shares the most common meaning of the word in second-century Latin: speculator does mean "bodyguard" in Suetonius, Claudius 35.1, Galba 18.1, Otho 5.2; Tacitus, Histories 1.24ff, 1.31, 3.43. In imperial Greek, spekoula/twr almost always refers to a military executioner (Gospel of Mark 6.27; Acta Alexandrin. 11.A2.12 (= P.Yale.inv. 1536); Vita (et sententia) Secundi, pp. 72-74, Perry edn; Acta Pauli, Martyrium Pauli 5 (late? second century); Martyrium Dasii 12, Athanasius Apol. sec. (contra Arianos) 8. This is also the meaning in ps.-Zonaras' Lexicon s.v.: sigma1633). Thus the Suda's definition is somewhat surprising.