Table 2.

Symbol description

Symbol	Description
x	Ranking
y	Additional term size
$S_{\mathrm{AVG}}$	Average value of the term similarity
$d_{\mathrm{x}}$	Expansion word
$S_{\mathrm{x}}$	Query similarity
$w_{\mathrm{p}}$	Target word
${\omega }_{\mathrm{context}}$	Mean vector obtained for each context word
V	Vocabulary
$Z_{\text{Bst}}\left(x\right)$	Best location on the search space
$Z_{\text{p}}\left(x\right)$	Mean location of Aquila in the current iteration $x$
$S$	Total number of iterations
$n$	Population size
$R_1$,$R_2$,$R_4$ and $R_5$	Random integer in the range [0, 1]
$Z_{\text{r}}\left(x\right)$	Random location of Aquila
$d$	Dimensionality
${\text{Levy}}_{\text{f}}$	Levy flight function
$R_3$	Total number of search cycles
$d_1$	Integer that lies within [1, d]
$\varpi$	Constant value (0.005)
p,q	Random numbers that are set as 0 and 1, respectively
$c$	Constant with a value of 0.001
$\alpha$	Constant with a value of 1.5
$\mathit{ub}$ and $\mathit{lb}$	The upper and lower bound values
${\text{Quality}}_{\text{f}}$	Quality function value
$C_{\text{oot}}{P}_{\text{os}}\left(j\right)$	Coot position
${\text{Leader}}_{P_{\text{os}}}\left(l\right)$	Selected position of the leader